1. Field of the Invention
The present invention relates to a charged particle beam writing method and a resizing method of a dimension variation amount, indicating a critical dimension (CD) difference, due to a loading effect, and more particularly to a method for calculating an electron beam dose to enhance a pattern line width uniformity in electron beam writing. Moreover, this invention is related to a resizing method of previously correcting a dimension variation amount due to a loading effect before inputting data into a pattern writing apparatus.
2. Description of the Related Art
Microlithography technique which forwards miniaturization of semiconductor devices is extremely important, because only this process performs forming a pattern in semiconductor manufacturing processes. In recent years, with an increase in high integration and large capacity of large-scale integrated circuits (LSI), a circuit line width required for semiconductor elements is becoming narrower and narrower. In order to form a desired circuit pattern on these semiconductor devices, a master pattern (also called a mask or a reticle) with high precision is required. Then, since the electron beam technique for writing or “drawing” a pattern has excellent resolution intrinsically, it is used for manufacturing such high precision master patterns.
FIG. 19 shows a schematic diagram describing operations of a conventional variable-shaped electron beam pattern writing apparatus. As shown in the figure, the variable-shaped electron beam pattern writing apparatus (EB (Electron beam) writing apparatus) includes two aperture plates and operates as follows: A first or “upper” aperture plate 410 has an opening or “hole” 411 in the shape of a rectangle, for example, for shaping an electron beam 330. This shape of the rectangular opening may also be a square, a rhombus, a rhomboid, etc. A second or “lower” aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired rectangular. The electron beam 330 that left a charge particle source 430 and has passed through the opening 411 is deflected by a deflector. Then, the electron beam 330 passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and irradiates a target workpiece or “sample” 340 mounted on a stage that is continuously moving in one predetermined direction (e.g. X-axis direction) during the writing. In other words, a rectangular shape capable of passing through both the opening 411 and the variable-shaped opening 421 is used for pattern writing of the target workpiece 340 mounted on the stage. This method of writing or “forming” a given variable shape by letting beams pass through both the opening 411 and the variable-shaped opening 421 is referred to as a “variable shaping” method.
In recent years, a chemically amplified resist is cited as one of resists often used for an electron beam exposure. The chemically amplified resist has a problem in that the optimal exposed dose changes because of a time elapsed, indicating to be left untouched, before and after the exposure. As a method of solving this problem, there is disclosed a technique that determines a change of resist sensitivity by measuring a film thickness, etc. of a corrected dose pattern and performs irradiation again by using a beam whose diameter is obscured to around 20 μm (refer to, e.g., Japanese Unexamined Patent Publication No. 2000-267259 (JP-A-2000-267259)).
As mentioned above, the chemically amplified resist has the problem that the optimal dose changes because of being left before and after the exposure. In other words, when the chemically amplified resist is used for manufacturing a mask, the line width critical dimension (CD) obtained after writing the mask being a target workpiece changes or “fluctuates” (PED). In the technique described in the Patent Document (JP-A-2000-267259) stated above, there is a problem in that highly precise correction cannot be performed since a dose error occurs with respect to each pattern category. Moreover, there is another problem in that a pattern for determining a corrected dose is needed and a film thickness measuring apparatus, an exposure assist chamber, etc. are also required in addition to an exposure apparatus body. There is a further problem in that the step of performing irradiation again becomes necessary.
It can be supposed that the line width dimension (CD) variation (PED) after writing the mask mentioned above is caused by a diffusion of acid generated by the writing. The acid diffusion occurs in a region of several tens nm, and its occurring rate is around 1.0 nm/h. On the other hand, in the electron beam writing, when electron beams irradiate a target workpiece, such as a mask, on which resist film is applied, there exists a factor, e.g., a fogging effect, causing a dimension variation or “fluctuation” of the resist pattern. The fogging effect is a phenomenon of an irradiated resist caused by a multiple scattering, namely, indicating that a backward scattering electron due to a proximity effect goes out of the resist to be scattered again at the lower part of the electron lens barrel included in a writing apparatus, and irradiates the mask again. The fogging affects a large area (from several mm to several cm). In addition, when etching a shading film etc. being a layer lower than the formed resist pattern as a mask, there exists a phenomenon called the loading effect which causes a dimension variation of the shading film to be etched. The amount of dimension variation due to the fogging effect or loading effect is also affected by the time elapsed after writing the mask.